The Beatles' "Hey Jude" concludes with one of pop music's most epic fade-outs.

Like the proverbial old soldier, some songs never die — they just fade away. Think of "Hey Jude," in which The Beatles hammer the closing refrain for more than three minutes before drifting into silence.

In a recent Slate article, music history and technology reporter William Weir says this used to be the popular way to end a pop song: Repeat your hook while the volume gradually eases off. Weir examined Billboard's Top 10 songs for every year since 1946 to see where the technique popped up.

"It peaked in 1985: Every one of the Top 10 songs of the year-end chart is a fade-out," he tells NPR's Robert Siegel. "By the 1990s, you start seeing a noticeable decline. It just gets worse for the fade-out after that."

In fact, Robin Thicke's "Blurred Lines" is the only major hit of the past several years to fit the bill. As NPR has covered before, the reason to add a fade-out varies from song to song. So, Weir says, does the artistry applied: The Beach Boys' "Caroline, No," for example, uses the opportunity to introduce a new element.

"Brian Wilson is meticulous about all recording aspects, so it shouldn't be surprising that he came up with some new ways to make the fade-out stand out," Weir says. "Just as you think you've heard everything in the song, this bass flute takes prominence in the last dwindling seconds. It really makes you pay attention all over again."

As studio tricks go, Weir says the fade-out is an easy one to pull off — but that hasn't always been the case. To learn how musicians created fades before modern recording technology, check out the radio version of this story at the audio link.